1) Yours is a very common situation, and I have rather long experience. I can tell you that if you have significant sagging, it is a mistake to avoid a breast lift. We have done a lot of revisions in women with sagging who just had implants, and were miserable afterwards.
2) The implant choice you mention sounds reasonable, but it is not your job to select the breast implants. That's part of what you pay your surgeon to do!
Your surgeon should put disposable implant SIZERS in your breasts during surgery, to see exactly what look a particular implant gives you. I think it is a mistake to make the final implant choice in advance. That's why it is important to have an inventory of different implants in the operating room.